switching mode power supply and a method of operating the power supply in a power save mode

ABSTRACT

A switching mode power supply and a method of operating the power supply in a power save mode. The switching mode power supply includes a first PWM controller and a second PWM controller that are driven by different driving voltages and control first and the second voltages to be output, respectively, a first transformer that is controlled by the first PWM controller to output the first voltage and having a primary coil, a secondary coil to induce the first voltage, and an auxiliary winding, and a rectifier that rectifies and smoothes a current flowing through the auxiliary winding of the first transformer, generates a power save mode voltage based on the respective driving voltages of the first and the second PWM controllers, and supplies the power save mode voltage to the first and the second PWM controllers. Accordingly, the power save mode is operated using a voltage difference without requiring an extra controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation or prior art application Ser. No.11/397,552, filed Apr. 5, 2006 in the U.S. Patent and Trademark Office,which claims priority from Korean Patent Application No. 2005-102073,filed on Oct. 28, 2005, in the Korean Intellectual Property Office, theentire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to a switching mode powersupply and a method of operating a power supply in a power save mode.More particularly, the present general inventive concept relates to aswitching mode power supply that outputs at least two voltages andoperates in a power save mode using a voltage difference when a minimumload is applied, and a method of operating in a power save mode.

2. Description of the Related Art

Since a conventional switching mode power supply (SMPS) operates aswitching element in a switching mode, it consumes less power. Also,since the SMPS uses a high frequency power transformer, the SMPS iscompact-sized and light-weight. It is possible for the SMPS to outputdifferent levels of direct current (DC) voltages at the same time. Forexample, if a printer employs the SMPS, it is possible for the printerto be supplied with a 3.3V or 5V (DC) voltage from a main power supplyand a 24V (DC) voltage supplied from a high voltage power supply or aprinter engine at the same time.

The SMPS enters a power save mode to minimize power consumption when thehigh voltage power supply or the printer engine that uses a high voltageis idle.

The conventional SMPS has at least two pulse width modulation (PWM)controllers and at least two transformers to output at least twovoltages. The conventional SMPS receives a PWM on/off signal to controlthe output of the high voltage to turn off the second PWM controllersuch that the high voltage is not output in the power save mode.

More specifically, if a SMPS is designed to output two voltages forexample, the SMPS includes two PWM controllers and two transformers.

It is assumed that a first PWM controller controls a low voltage outputand a second PWM controller controls a high voltage output.

The first PWM controller outputs a PWM signal, and a first transistorswitches on/off according to the PWM signal and thereby regulates acurrent flowing through a primary coil of a first transformer, and thuscontrols a voltage induced at a secondary coil of the first transformer.The voltage induced at the secondary coil at the first transformer isrectified, smoothed, and then output to a first output terminal as thelow voltage. The second PWM controller and a second transistor generatea voltage in the same manner as described above and output the voltageto a second output terminal as the high voltage.

The conventional SMPS requires an external controller to output the PWMon/off signal to control the high voltage output from the second PWMcontroller to turn on/off (i.e. from on to off) when entering a powersave mode. When receiving the PWM on/off signal from the externalcontroller, the second PWM controller is shut down according to thereceived PWM on/off signal. That is, the second PWM controller stopsoutputting the high voltage when the PWM on/off signal is received.

That is, the SMPS has to receive the control signal in order to operatein the power save mode. Accordingly, the SMPS also requires the externalcontroller to output the control signal.

SUMMARY OF THE INVENTION

The present general inventive concept provides a switching mode powersupply to operate in a power save mode using a voltage differencegenerated internally without requiring an external controller to outputa control signal in order to operate in the power save mode, and amethod of operating in the power save mode thereof.

Additional aspects of the present general inventive concept will be setforth in part in the description which follows and, in part, will beobvious from the description, or may be learned by practice of thegeneral inventive concept.

The foregoing and/or other aspects of the present general inventiveconcept are achieved by providing a power supply which outputs a firstvoltage and a second voltage, including a first pulse width modulation(PWM) controller and a second PWM controller that are driven bydifferent driving voltages to control the first and the second voltagesto be output, respectively, a first transformer that is controlled bythe first PWM controller to output the first voltage, the firsttransformer including a primary coil, a secondary coil, and an auxiliarywinding, and a rectifier that rectifies and smoothes a current flowingthrough the auxiliary winding of the first transformer, generates apower save mode voltage based on the respective driving voltages of thefirst and the second PWM controllers, and supplies the power save modevoltage to the first and the second PWM controllers.

The power save mode voltage generated by the rectifier may be greaterthan or equal to the driving voltage of the first PWM controller, andthe power save mode voltage may be less than the driving voltage of thesecond PWM controller.

The second PWM controller may be powered off by the power save modevoltage.

In the power save mode, an output terminal connected to a secondary coilof the first transformer may have a minimum load, and the rectifier maygenerate the power save mode voltage using a reduced current of thefirst transformer.

The power supply may further include a voltage lowering unit that lowersthe power save mode voltage generated by the rectifier and supplies thelowered voltage to the second PWM controller.

The voltage lowering unit may include a first end connected to therectifier and a second end connected to the second PWM controller.

The voltage lowering unit may either be a variable resistor or aregulator.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a power supply switchable betweena power save mode and a normal driving mode, the power supply includinga first output unit, a second output unit, a PWM controller unit tocontrol the first output unit to output a first output voltage in thepower save mode and in the normal driving mode, and to control thesecond output unit to output a second output voltage in the normaldriving mode and not to output the second voltage when in the power savemode, and a sensing unit to sense a load applied to at least one of thefirst and second output units and to select one of the power save modeand the normal driving mode based on the sensed load.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a switching mode power supplyusable with a high voltage power supply (HVPS) and/or a printer engine,the switching mode power supply including first and second output units,first and second transformers to provide first and second voltages tothe first and second output units, respectively, a first PWM controllerto drive the first transformer, a second PWM controller to drive thesecond transformer, and a sensing unit to drive the first and second PWMcontrollers using a driving voltage that is determined based on a loadapplied to at least one of the first and second output units.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a switching mode power supply,including at least two output units to output different voltage levelsincluding a high voltage, and a PWM switching unit to sense a loadapplied to the output units and to power OFF the output unit thatoutputs the high voltage when the load is determined to be a first loadand to power ON the at least two output units when the load isdetermined to be a second load.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a power supply, including atleast two output units to output different voltage levels including ahigh voltage, at least two PWM controllers that are drivable bydifferent voltages, and a sensing unit to sense a load applied to theoutput units and to power OFF the PWM controller that drives the outputunit that outputs the high voltage when the load is determined to be ina first load state and to power ON the at least two PWM controllers whenthe load is determined to be in a second load state.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a method of operating a powersupply in a power save mode, the method including a first transformer tooutput a first voltage and having a primary coil, a secondary coil onwhich the first voltage is induced, and an auxiliary winding, and asecond transformer to output a second voltage, and a first PWMcontroller and a second PWM controller that are driven by differentdriving voltages and control outputs of the first and the secondtransformers, respectively. The method includes rectifying and smoothinga current flowing through the auxiliary winding of the firsttransformer, generating a power save mode voltage based on therespective driving voltages of the first and the second PWM controllersusing the rectified and smoothed current of the auxiliary winding, andsupplying the generated power save mode voltage to the first and thesecond PWM controllers.

The power save mode voltage may be greater than or equal to the drivingvoltage of the first PWM controller, and the power save mode voltage maybe less than the driving voltage of the second PWM controller.

The method may further include lowering the power save mode voltageusing either a variable resistor or a regulator and supplying thelowered power save mode voltage to the second PWM controller.

The foregoing and/or other aspects of the present general inventiveconcept are also achieved by providing a method of operating a powersupply in a power save mode, the method including automaticallyselecting a power supply mode using a difference between drivingvoltages to drive at least two PWM controllers that control the powersupply to output at least two voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the present general inventive concept willbecome apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a circuit diagram illustrating a SMPS to operate in a powersave mode according to an embodiment of the present general inventiveconcept; and

FIG. 2 is a circuit diagram illustrating a SMPS to operate in a powersave mode according to another embodiment of the present generalinventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to the likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures.

FIG. 1 is a circuit diagram illustrating a SMPS to operate in a powersave mode according to an embodiment of the present general inventiveconcept.

The SMPS powers on/off an output voltage using a voltage difference whena minimum load is applied, thereby operating in a power save mode.

Referring to FIG. 1, the SMPS includes a first rectifier 110, a firstPWM controller 120, a first transistor Q1, a first transformer 130, asecond rectifier 140, a third rectifier 150, a second PWM controller160, a second transistor Q2, a second transformer 170, and a fourthrectifier 180.

The first rectifier 110 rectifies an alternating current (AC) voltageinput from an AC power supply using, for example, a bridge diode DM1 anda capacitor C1.

The AC voltage rectified by the first rectifier 110 is applied toprimary coils of the first transformer 130 and the second transformer170. The first transformer 130 induces a voltage on a secondary coilusing interaction between the primary coil and the secondary coil. Thefirst PWM controller 120 outputs a first PWM signal to output a lowvoltage, and the first transistor Q1 switches on/off according to thefirst PWM signal, thereby regulating a current flowing through theprimary coil of the first transformer 130. Accordingly, the voltageinduced on the secondary coil of the first transformer 130 can becontrolled according to the first PWM signal.

The first transistor Q1 switches on/off according to the first PWMsignal output from the first PWM controller 120.

The second rectifier 140 rectifies and smoothes the voltage induced onthe secondary coil of the first transformer 130 using, for example, adiode D1 and a capacitor C2, and outputs the rectified and smoothedvoltage to a first output terminal (output1). The voltage output to thefirst output terminal (output1) is the low voltage.

The third rectifier 150 rectifies and smoothes a current flowing throughan auxiliary winding of the first transformer 130 using, for example, adiode D2 and a capacitor C3, thereby generating a Vcc. The thirdrectifier 150 supplies the generated Vcc to the first and the second PWMcontrollers 120 and 160 as a driving voltage Vcc.

The first and the second PWM controllers 120 and 160 are driven by theVcc supplied from the third rectifier 150, and the first and second PWMcontrollers 120 and 160 generate the first PWM signal and a second PWMsignal, respectively.

The second transformer 170 receives the voltage from the first rectifier110 onto the primary coil thereof to induce a voltage on the secondarycoil of the second transformer 170 using an interaction between theprimary coil and the secondary coil. The second PWM controller 160outputs a second PWM signal to output a high voltage, and the secondtransistor Q2 switches on/off according to the second PWM signal,thereby regulating a current flowing through the primary coil of thesecond transformer 170. Accordingly, the voltage induced on thesecondary coil of the second transformer 170 can be controlled accordingto the second PWM signal.

The second transistor Q2 switches on/off according to the second PWMsignal output from the second PWM controller 160.

The fourth rectifier 180 rectifies and smoothes the voltage induced onthe secondary coil of the second transformer 170 using, for example, adiode D3 and a capacitor C4, and outputs the rectified and smoothedvoltage to a second output terminal (output2). The voltage output to thesecond output terminal (output2) is the high voltage.

The third rectifier 150 generates a normal driving voltage as thedriving voltage Vcc to drive the first and the second PWM controllers120 and 160 in a normal driving mode, and the third rectifier 150generates a power save mode voltage as the driving voltage Vcc to enterthe power save mode. The first and the second PWM controllers 120 and160 use different driving voltages. The first PWM controller 120 uses alow level driving voltage, since the first PWM controller 120 outputsthe first PWM signal to output the low voltage, whereas the second PWMcontroller 160 uses a high level driving voltage, since the second PWMcontroller 160 outputs the second PWM signal to output the high voltage.Accordingly, in the normal driving mode, both the first and the secondPWM controllers 120 and 160 are driven (i.e., driven normally), and inthe power save mode, the second PWM controller 160 that uses the highlevel driving voltage is powered off, and only the first PWM controller120 is driven.

For example, the first PWM controller 120 may use a driving voltage of12V and the second PWM controller 160 may use a driving voltage of 15V.Other voltages may alternatively be used. In the normal driving mode,the third rectifier 150 may generate the Vcc of 15V at a minimum tonormally drive the first and the second PWM controllers 120 and 160. Thefirst and the second PWM controllers 120 and 160 are normally driven bythe voltage 15V.

In the power save mode, the first and the second output terminals(output1 and output2) have a minimum load applied thereto. Accordingly,a low level of current flows through the auxiliary winding of the firsttransformer 130 that is connected to the first output terminal (output1)such that the third rectifier 150 generates the Vcc of 12V at a maximum,which is lower than the 15V in the normal driving mode. Accordingly, thesecond PWM controller 160, which is to be driven by the voltage of 15V,is powered off and enters the power save mode.

In other words, when the minimum load is applied to the first and/orsecond output terminals (output1 and output2), current induced in theauxiliary winding of the first transformer 130 is reduced such that thedriving voltage Vcc generated by the third rectifier 150 is a power savemode voltage (e.g., 12V) that corresponds to a voltage that is highenough to drive the first PWM controller 120, but is not high enough todrive the second PWM controller 160. The current induced in theauxiliary winding of the first transformer 130 may result frominteractions with the primary and/or secondary coil of the firsttransformer 130. More specifically, the current flowing through theauxiliary winding of the first transformer 130 may be a function of theload applied to the first output terminal (output1) on the secondarycoil side of the first transformer 130. For example, the current inducedin the auxiliary winding of the first transformer 130 may beproportional to the load applied to the first output terminal (output1).The minimum load may be applied to the first output terminal (output1)or the first and second output terminals (output1 and output2) when ahigh voltage power supply that uses the high voltage output by thesecond output terminal (output2) or a printer engine that is connectedto the first output terminal (output1) is idle. Thus, the auxiliarywinding of the first transformer 130 and the third rectifier 150 canautomatically switch the SMPS into the power save mode by sensing theload applied to first and second output terminals (output1 and output2)without requiring an external control signal produced by an externalcontroller. In other words, the auxiliary winding of the firsttransformer 130 may function as a sensing unit to sense the load that isapplied to the output of the SMPS in order to generate the properdriving voltage Vcc for the first and second PWM controllers 120 and160.

FIG. 2 is a circuit diagram illustrating a SMPS to operate in a powersave mode according to another embodiment of the present generalinventive concept.

Referring to FIG. 2, the SMPS includes a first rectifier 210, a firstPWM controller 220, a first transistor Q1, a first transformer 230, avoltage lowering unit 255, a second rectifier 240, a third rectifier250, a second PWM controller 260, a second transistor Q2, a secondtransformer 270, and a fourth rectifier 280.

Since the first rectifier 210, the first PWM controller 220, the firsttransistor Q1, the first transformer 230, the second rectifier 240, thethird rectifier 250, the second PWM controller 260, the secondtransistor Q2, the second transformer 270, and the fourth rectifier 280may be similar to those corresponding elements of the SMPS of theembodiment of FIG. 1, detailed descriptions thereof will not beprovided.

The voltage lowering unit 255 is disposed between the third rectifier250 and the second PWM controller 260 and uses a voltage differencebetween a driving voltage applied as a Vcc to the second PWM controller260 and a driving voltage applied as a Vcc to the first PWM controller220. More specifically, the voltage lowering unit 255 lowers the drivingvoltage applied from the third rectifier 250 to the second PWMcontroller 260 to create a greater difference between the drivingvoltages applied from the first PWM controller 220 and from the secondPWM controller 260.

In the power save mode, the third rectifier 250 generates a lower levelvoltage as the driving voltage Vcc than in a normal driving mode similarto the third rectifier 150 of FIG. 1. The voltage lowering unit 255further lowers the low level voltage output as the driving voltage Vccsupplied from the third rectifier 250 to the second PWM controller 260.Accordingly, the second PWM controller 260, being applied with thedriving voltage Vcc lowered by the voltage lowering unit 255, is poweredoff and enters the power save mode. The auxiliary coil of the firsttransformer 230 may operate in a similar manner as described above withrespect to the auxiliary winding of the first transformer 130 of FIG. 1.

For example, the voltage lowering unit 255 may be realized by anadditional circuit such as a variable resistor or regulator to lower thedriving voltage Vcc generated by the third rectifier 250.

In the embodiments of the present general inventive concept, the SMPSoutputs two voltages and can operate in a power save mode to generateone output voltage. However, this arrangement should not be consideredas limiting the scope of the present general inventive concept. Themethod of operating in the power save mode may be applied to a SMPS thatoutputs more than two voltages.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

1. A power supply apparatus, comprising: a plurality of pulse widthmodulation (PWM) controllers; a transformer which is configured with aprimary coil, a secondary coil, and an auxiliary coil; and a rectifierwhich generates a power save mode voltage using a current flowingthrough the auxiliary coil, supplies the power save mode voltage to theplurality of PWM controllers, and turns off at least one of the PWMcontrollers if a power save mode is executed.
 2. The power supplyapparatus as claimed in claim 1, wherein the current flowing through theauxiliary coil is determined according to load at an output end of thetransformer.
 3. The power supply apparatus as claimed in claim 1,wherein driving voltages of at least two PWM controllers of theplurality of PWM controllers are different from each other.
 4. The powersupply apparatus as claimed in claim 1, wherein the power save modevoltage is equal to or greater than a driving voltage of at least one ofthe plurality of controllers, and less than a driving voltage of atleast one of the plurality of controllers.
 5. The power supply apparatusas claimed in claim 1, further comprising: a voltage lowering unit whichlowers the power save mode voltage generated by the rectifier.
 6. Thepower supply apparatus as claimed in claim 5, wherein the voltagelowering unit comprises one end connected to the rectifier and the otherend connected to at least one of the plurality of PWM controllers, andsupplies the lowered voltage to at least one of the plurality of PWMcontrollers.
 7. A control method of a power supply apparatus, the powersupply apparatus having a plurality of pulse width modulation (PWM)controllers and a transformer which is configured with a primary coil, asecondary coil, and an auxiliary coil, the method comprising;generating, by a rectifier, a power save mode voltage using a currentflowing through the auxiliary coil; and supplying the power save modevoltage to the plurality of PWM controllers, and turning off at leastone of the PWM controllers if a power save mode is executed.
 8. Thecontrol method as claimed in claim 7, wherein the current flowingthrough the auxiliary coil is determined according to load at an outputend of the transformer.
 9. The control method as claimed in claim 7,wherein driving voltages of at least two PWM controllers of theplurality of PWM controllers are different from each other.
 10. Thecontrol method as claimed in claim 9, wherein the power save modevoltage is equal to or greater than a driving voltage of at least one ofthe plurality of controllers, and less than a driving voltage of atleast one of the plurality of controllers.
 11. The control method asclaimed in claim 7, further comprising: lowering the power save modevoltage generated by the rectifier; and supplying the lowered voltage toat least one of the plurality of PWM controllers.